Good day all,

I will be trying to replace my TCM to see if that clears a hard code for 0720 output speed sensor changed the sensor 3 times and still there so i might as well buy a TCM

will I need to program and if I can or is it dealer exclusive??

 

In my experience with a Volvo S40 2008 where a transmission was changed, it is necessary to maintain the same TCM.
The TCM that was installed in the "new" transmission only allowed emergency operation of the car., I don´t know if it is the same for all models and years of Volvo, I understand it i only made by the dealer

 

year and model/transmission?

Are you sure its the TCM? Have you checked the signal at the TCM connector? have you checked voltage/ground to the output speed sensor? have you checked the input speed sensor voltage/ground? I'd start by testing at the TCM then clean the contacts and reseat the connector and inspect the wiring and ground points.

The good news is there's plenty of used units on eBay - but newer model years may require software pairing to talk to your ECU. Xemodex sells a software transfer service but for some reason the S40 is not on their list of supported Volvos.

 

XemodeX doesn't cover TCMs that aren't under the hood with the ECU it seems.

 

I have tried to find a pinout schematic that would tell me about the voltage at the sensor Its only 2 wires (VSS) and I cannot find what the voltage at the wires should be?

would i check each pin with a meter and get what the voltage should be ? meter with ground to battery and check both pins for reading?

From the harness where the sensor connects to should correspond with a pin at the TCM harness (while TCM is removed) how to check for connectivity?

The TCM I have removed, and which would be the pin number that matches that sensor i keep getting a 0720 Output Speed Sensor Circuit code even after changing the sensor with an OEM one

 

On most cars, most of the time, the wire color at the plug (in this case, the TCM plug) should be the same at the sensors it connects to. That may well narrow it down so you can figure out where those wires come into the TCM plug.

If it was me (being the world's laziest troubleshooter, always looking for the cheap, easy way out), I'd pull the plug at the sensor and short the two lines together (using alligator clips or a bent paper clip - whatever is appropriate for the pins in the sensor connector). Then I'd look for where those wires come into the TCM plug (using wire color as a guide) and see if they read shorted. If not, something is open in between the two plugs.

 

Well after an hour of the 5000 page volvo manual i find that the 2 wires from the VSS go to pins 9 and 10 to the TCM

what would be a good connectivity tester to ensure no break in the harness ? being that the TCM is inside tthe car and sensor harness is under the hood?

Still cannot find what the voltages supposed to be at the harness for the VSS ?

 

lol sounds like a plan but i found the 2 pin location on the TCM now trying to see if theres a direct connection to the 2 plugs of the sensor
i used to have a universal wire tester to see if the wire is broken or open but i lent it out and the person lost it similar but way cheaper than the ones electricians used in circuits in a house to thr panel
trying elimenate if its the harness or the TCM

 

It's not your TCM, sorry -

Even it is was, the NEW tcm would probably need a software download (using VIDA) to make it talk to the rest of the car.

 

I am hoping its not my TCM but i cant clear this 0720 code output sensor circuit even with a brand new oem sensor ?
i have tested everything exceot for communication from sensor to TCM POSSIBLY a damaged harness or plug
i have cleaned the connections between harness and TCM clean it out with deoxit and hard roothbrush

 

one other thought - doing some Internet readings on the nature of this code and it was suggested the TCM is calculating a differential between the input and output sensors. Seems plausible to me that there could be an issue with the input sensor as well. Curious if the VIDA diagnostic procedure includes testing the input sensor.

 

Very odd it seems to just give thst one code 0720 the other sensir was replaced last year and i have a new one coming today

just trying to test if the sensor circuit to the tcm is kinked or damaged i have the tcm out and will short the sensor plug and hopefully i get continous path instead of open as the code states

last resort maybe the TCM is shot this is the second time in a year chasing this code down ??

btw the other sensor is also labeled as the crankcase sensor or aka the automatic transmission sensor go figure

 

Irivera1342, the process for checking the wires you're asking about is in my previous post. Just use a plain ol' ohmmeter (a feature in pretty much any multi-meter, including the uber-cheap Harbor Freight versions) to check for continuity - by shorting out one end of the two wires, and checking the other end, you'll know definitively whether the wires are good or not. Short one end, and the other end measures zero ohms (or close). Remove the short, and the ohmmeter measures open (infinite resistance).

 

Hey thanks I was attempting to short the pins at the sensor harness and i couldn't find something small enough that would stay in place without damaging the female plugs (didnt want to make them holes larger and then need a new harness lol)

so i got one of the replacement sensors that I was about to throw out, cut the sensor plug away and used the wires as a perfect jumper since it matches the female harness without issue !!!
then went inside of the car tested pins 9 and 10 and had connectivity between .3-.5 but steady .4 if if don't move my hands much everything else was open as it should be not interrupting this circuit
Odd for the TCM to report output speed circuit code 0720

I will put the TCM back and check for voltages at the sensor if the wires are good then I should get power at the plug if not then something is open inside of the TCM

 

Since the connector for the sensor doesn't provide for ground, you may want to check/clean up the ground wire to the transmission...

 

Damn i just spent 3 hours putting everything uder the hood back battery try air filter box and intake hose i did clean the negative from battery to chasis and that was spotless wonder where is that ground strap for the tranny

exact thing happen to 2 of my grand cherokee jeeps ground to tranny was soaked in oil and corrode giving badsignals to shifting solenoids grr

 

update

Since the code kept triggering 0720 outputs speed sensor circuit and after testing the circuit for connectivity and communication I purchased a TCM from ebay
100k for original OEM and 20k miles for another 2 replacements (OEM), on the last replacement it immediately triggered the check engine up flashing light on an OEM sensor without even driving

TCM replacement no programming whats so ever, exact model and series for 25.00 with free shipping

After installing and turning on the car immediately the code cleared !!!

Drove the car for about 40 miles not a single blip actually shifts faster and firmer and a significant alot less time between shifts slipping like before
, it seems the TCM was on the way to failure last 10 months and finally did.

several shout outs to the senior and super moderator who kept my insanity in check several things was definitely learned

The Tranny has only 3 replaceable sensors and ALL ARE within 2 feet of each other lol
Vehicle Speed Sensor output ( white plastic connector at the multi bracket section
Automatic Transmission Speed Sensor/ Engine Speed Sensor/Crankshaft sensor (input) (black plastic connector

The above 2 are the same sensor except for color of connecting tab, length of connection about 3 inches vs 5 and PRICE lol

PNP aka Gear Selector no special alignment tool needed just line up the marker on the sensor to the stationary bolt/stub??

to get to them it takes maybe 20 minutes if you remove the air filter box and the rubber hose and to get to the input sensor you have to remove one of the 2 (I did both) battery negative cables seems like one goes on top of the tranny housing and the other to the chassis again all within 3 feet of each other
again I hope this helps someone else if they are stuck on a 0720 code and it wont clear PS each and every time it also triggers the 0700 code which correlates to an issue or code within the TCM

 

thanks for the update, glad you were able to work the process to a happy resolution!